Astra 1.4i Mk3 Running problems

[Madmalx]

Anyone got any ideas on a fault on my dad's 1995 1.4i Astra? It starts fine, runs ok, then as it warms up it starts popping slightly through the exhaust and it gains a hesitation when you try to rev it and it's down on power. Changed the distributor cap, rotor arm, plugs and checked the timing belt allignment - no probs. Oxygen sensor is switching, but if I disconnect it, it makes no difference to the running. Swapped the MAP sensor for a spare I had, and the temp. sensor too but still no joy. Anyone got any ideas???

[Jacko lah]

I had something similar and it turned out to be the insides of the Cat had started to fall apart. It was okay up to 3000 RPM, but then it was really flat (I assume that the higher the exhaust gas flow the more the matrix was pushed like a cork)
Also the higher the RPM the more Exhaust noise was as it was trying to escape from the manifold to down pipe flexy joint.

Might be this. If it is this take the cat off and remove all the insides with a pole and a hammer - It will fail the next MOT but you can pick a pattern Cat up for 65 quid. (I have the old box in my garage!)

[Madmalx]

Problem solved!!! Rang our local dealer and spoke to one of the mechanics, suggested the common problems of the Coolant Temp sensor and the Cat but also suggested that the woodruff key on the timing gear could be damaged causing the bottom gog to be out a little, and it was. Unfortunately it's damaged the crankshaft end so it was either a crank out job, or wedge a piece into the gap that has been created, so I've done the latter as a temporary measure.